Possible Sources of Iron Nuclei in Ultra-High-Energy Cosmic Rays

The origin of a cosmic ray particle with an ultra-high energy of 2.44 x 10 20 eV recorded by the Telescope Array is discussed by assuming that it is a heavy nucleus, namely an iron or silicon nucleus. Iron is chosen as a heaviest element in cosmic rays, while silicon is chosen to find out how much the theoretical results obtained vary with the mass of the heavy nucleus. Assuming extragalactic origin of the particle with such energy, the constraints on the distances to possible sources are analysed using a routine calculation of the cosmic ray propagation in extragalactic space. These possible sources are discussed.